#include <bits/stdc++.h>
using namespace std;
typedef long long ll;

ll f[110];
/**
 * 
 * 时间复杂度 O(n)
 * 空间复杂度 O(1)
 * 
 * 斐波那契数列
 * 
 */
int main() {
    ll n;
    cin >> n;
    f[1] = f[2] = 1;
    for (int i = 3; i < 50; i++) {
        f[i] = f[i - 1] + f[i - 2];
    }
    cout << f[n] << endl;
    return 0;
}